Semi-transparent small molecule organic solar cells with laminated free-standing carbon nanotube top electrodes

We have developed semi-transparent n–i–p organic solar cells (OSC) with free-standing multi-wall carbon nanotube (f-CNT) sheets as transparent top electrodes. By a simple and damage-free room temperature orthogonal liquid solution assisted self-laminating process, f-CNT top electrodes are successfully deposited on top of ZnPc:C60 bulk heterojunction small molecule OSCs. The cells show high fill factors above 58% as well as efficiencies up to 1.5% and greater long-term stability compared to the device having a metal electrode. For the given cell structure with f-CNT semi-transparent electrodes, the influence of an optical spacer on light absorption is studied by a systematic variation of the hole transport layer thickness, supported by optical simulations. The results strongly indicate that OSCs with f-CNT top electrodes and optimized thin film stack are highly promising for semi-transparent OSCs, which can be used in tandem devices, in tinted smart windows, and similar applications by a simple and damage-free process in roll-to-roll configuration that can be scaled to large area manufacturing.

Graphical AbstractSemi-transparent organic solar cells laminated with free-standing carbon nanotube top electrodes.Figure optionsDownload as PowerPoint slideHighlights
► We have developed semi-transparent small molecule organic solar cells with free-standing carbon nanotubes (CNT) top electrodes.
► Top CNT electrodes are deposited on devices using an orthogonal liquid solution assisted self laminating process, which is simple and damage-free for organic layers.
► Devices show very low leakage currents, high fill factors, promising efficiencies, transparencies, and long-term stability.
► Influence of an optical spacer on light absorption is studied by a systematic variation of the hole transport layer thickness.